This is an application for a supplement to a broadly based inter-disciplinary, interdepartmental program project on the physiological basis of pulmonary disease. The chief emphasis is on fundamental aspects of the functions of the lung, including marine mammals. The post-dive oxygen debt may be much less than the oxygen deficit incurred during diving in seals. We believe that the metabolic basis for the apparently small oxygen debt may be assessed best by determining the metabolic fate of lactate during recovery from a dive. We propose to measure lactate turnover and the fraction of lactate oxidized to CO2 and H2O, reduced to glucose, or converted to alanine. Radioactive L-14C-lactate will be infused into catheterized seals, Phoca vitulina, immediately following 10-15 minute restrained dives. Oxygen consumption and expired 14CO2 specific activity will be measured with an on-stream analyzer complex consisting of a proportional counter with rate meter, a gas flow meter, a carbon dioxide analyzer, and an oxygen analyzer. The concentration and specific activity of lactate, glucose, and alanine in serial blood samples collected throughout recovery will be determined by enzymatic spectrometric analysis and liquid scintillation counting after suitable metabolite isolation by ion-exchange chromatography. Data analysis will show the fraction of lactate oxidized, reduced to glucose, or converted to alanine. Lactate production during a dive will be measured as described by Karlsson (1971) and the anaerobic energy production (lactacid oxygen deficit) calculated. In addition, the lactacid oxygen debt will be calculated from the lactate production and the fraction of lactate reduced to glucose. The pattern of glycogen depletion in skeletal muscle during successive dives will be determined from muscle biopsies. In addition, muscle lactate and alanine concentrations will be measured for the biopsies using standard techniques. These experiments using seals represent the first attempt to understand how lactate metabolism influences the oxygen debt and are fundamental to our understanding of similar processes in other species, including man.